The present invention relates to a method for producing separating nozzle elements composed of a separating body and cover plates for the separation of gaseous or vaporous mixtures. Gaseous or vaporous mixtures are understood to mean particularly isotope mixtures such as .sup.235 UF.sub.6 and .sup.238 UF.sub.6 which, due to their chemical properties, make particular demands on the material of the separating nozzle elements.
In the separating nozzle process, the gas pressure corresponding to the minimum specific energy consumption is inversely proportional to the characteristic dimensions of the separating nozzles,as described in the publication Chemie Ing. Technik 39 (1967), at page 4. Since the costs for compressors, pipelines, valves and control devices required to perform this process decrease considerably with increasing gas pressure, the characteristic dimensions of the separating nozzles must be selected to be as small as possible. The narrowest widths of the separating slits in separating nozzles encountered today are between 10 and 3 .mu.m, which corresponds to presently employed or desired inlet pressures of between 0.5 and 1.5 bar.
To produce separating nozzle elements having particulary small characteristic dimensions it is known to assemble the separating nozzle elements from separating bodies and cover plates. The separating bodies are then penetrated by separating nozzles and gas conduits, while the cover plates include channels for the intake and discharge of the gas or vapor streams.
At the locations where the slit-shaped separating nozzles are terminated by the cover plates, there occurs, of course, a deceleration of the gas stream which is determinative for the separation and results in a loss of separating output. This loss is the greater, the smaller the ratio of the thickness of the separating body to the narrowest width of the separating slit, or separating body aspect ratio. To keep separating output losses sufficiently low, separating body aspect ratios of between 100 and 200 must be approached. With a value of 3 .mu.m for the narrowest width of the separating slit, the separating bodies should thus have a thickness of between 300 and 600 .mu.m.
Separating bodies having such aspect ratios of this order of magnitude and narrowest widths of a few microns for their separating slits can be produced, in principle, by partially irradiating a plate or laminar material, i.e. mold material, whose properties can be altered by high energy radiation, and partially removing mold material based on the altered properties resulting from the irradiation so as to produce a mold containing openings defining the separating nozzles and gas conduits, and then filling the openings with a material compatible with the mixture to be separated (structure material) whereupon the mold material is removed.
In the practical application of this basic principle, however, the problem is encountered that the high energy radiation which penetrates a mold material layer of the desired thickness of the separating body (300 to 600 .mu.m, as discussed above) causes secondary processes in the presently known materials and these secondary processes worsen the spatial resolution capability to such a degree that the required tolerances for the narrow separating slits are not realized with certainty.
German Pat. No. 2,922,642, corresponding to Becker et al U.S. application No. 155,652 filed Jun. 2nd, 1980, issued Dec. 27, 1983 as U.S. Pat. No. 4,422,905, therefore discloses a separating element composed of a plurality of stacked plates which, each by itself, may have a much smaller aspect ratio. Aside from the fact that the requirements for precision in mutually aligning the plates to be stacked and their mutual sealing constitute engineering problems, this method requires that the material forming the separating nozzles and gas conduit be contiguous in space and this may lead to technical and economical drawbacks.
German Pat. No. 2,933,570, and counterpart U.S. Pat. No. 4,351,653 to Becker et al, propose that individual layers of the mold material be placed on top of one another in steps until the desired total thickness of the separating body is reached and each layer, after having been partially irradiated and having parts of the mold material removed, is filled with structure material. This eliminates the sealing problems and it becomes possible to achieve separating bodies in which the material forming the separating nozzles and gas conduits is not spatially contiguous, as shown in FIGS. 7 and 8 of the above patents.
The stepwise application of the mold material and the stepwise filling with structure material is relatively complicated.